Many pressure vessels or pressurized reactors used in the chemical process industries require that means be provided to either heat or cool the vessel. To satisfy this requirement, it has been conventional practice to weld a temperature control jacket to the reactor vessel thereby defining an annular space around the vessel through which a heat transfer fluid can be circulated.
Pressure vessels which operate at a relatively low pressure are usually made from welded steel plates. Generally, the welding of a temperature control jacket to such a vessel presents no difficulties since the vessel is made of a grade of steel which is suitable for welding.
However, in the case of vessels and reactors which contain high pressures, different constructions are employed in order to withstand safely the associated high operating pressure levels. For example, pressure vessels which contain pressures greater than 5,000 psi generally include walls of a substantial thickness, e.g. greater than 3 inches, and the materials which comprise the vessel wall are usually high strength, alloyed steels rather than plain carbon steels. As a result, the material used for the construction of such pressure vessels is not well suited for welding.
Increasingly, vessels for operating at high pressures, e.g. pressures greater than 5,000 psi, are manufactured by forging the entire body from a single high strength alloyed steel ingot, thus eliminating the need for any welding of the vessel structure. However, the necessity of a temperature control jacket still exists and it has been the practice to machine suitable projections on the outside of the vessel body and then weld a temperature control jacket to such projections. However, there are a number of problems associated with such a manufacturing technique and the resulting product. For example, because the vessel material is not optimally suited for welding, extensive pre-welding preparation is required, such as buttering, as well as carefully controlled preheating, in order to insure that the weld is made at a specific elevated temperature. After the weld has been made, an equally extensive post weld heat treatment must be provided. Notwithstanding all these precautions, there is a significant tendency for weld cracks to form and such cracks, although seemingly local anomalies at the jacket welds, may grow and propagate into the main body of the vessel thereby causing a premature failure.
The invention disclosed herein provides an effective solution to the problem of welding a temperature control jacket to a high pressure reactor vessel wherein the vessel is constructed of a material which is not well suited for welding.